X-ray fluorescence is a measurement and analysis method in which incident X-rays coming from an X-ray source are allowed to hit a sample, causing electrons in the inner shells of constituent atoms to achieve excited states. When these excited states relax, the sample material emits fluorescent radiation at characteristic energies. Measuring the intensity and spectral characteristics of the fluorescent radiation with a detector allows deducing various facts about the material composition of the sample.
X-ray fluorescence analysis is commonly used for scrap sorting and other needs of metal industry, to quickly identify the composition of alloys. Problems may arise with light element constituents such as Mg, Si, Al, and others, because some of the characteristic X-ray fluorescence radiation of these elements comes at energies of only few keV (kiloelectronvolts). For example the K alpha line of Mg at 1.25 keV experiences heavy attenuation in air, so that in an analyzer device with an air gap of 0.9 cm between the sample and the detector something like 88% of the Mg-K radiation is attenuated before reaching the detector.
A prior art publication U.S. Pat. No. 6,909,770 B2 (Schramm et al.) discloses an X-ray fluorescence analyzer equipped with a chamber at the front part of the device, where the X-ray source and detector are located. The front wall of the chamber defines an opening, with a sealing mechanism around its edge. The sealing is pressed against a solid sample surface, which closes the chamber. A separate pump attached to the analyzer device draws all air out of the chamber. As examples of achieved conditions the document mentions a pressure range of 1 to 10-7 torr, or a more narrowly defined range of 1 to 10-2 torr. This reduces significantly the attenuation of X-rays in the free space between the sample and the detector, so said prior art device achieves a remarkable improvement in measuring fluorescent radiation at low energies.
A disadvantage of the prior art device is the additional clumsiness that the external pump arrangement introduces. The pump arrangement also draws a significant amount of electric energy, so that it needs a direct connection to an electric wall outlet. Therefore the apparatus is not well suited for field conditions. Additionally the apparatus is only applicable for analysing samples that have a smooth, solid outer surface, because otherwise it is impossible to seal the front end of the chamber tightly against the sample.